This invention generally relates to locking apparatus and more particularly relates to a segmented instrumentation tube including a locking sleeve for interlocking the segments of the instrumentation tube, so that the threaded ends of the instrumentation tube do not unthread when subjected to vibration, such an instrumentation tube being suitable for use in a nuclear power reactor pressure vessel.
Before discussing the current state of the art, it is instructive first to briefly describe the structure and operation of a typical nuclear power reactor, which contains instrumentation tubes. In this regard, a nuclear power reactor is a device for producing heat by the controlled fission of fissile material. The fissile material is in the form of fuel pellets disposed in an elongated hollow rod which serves as cladding for the fuel pellets. A plurality of the elongated fuel rods are bundled together by a plurality of spaced-apart grids having open cells therein for receiving each fuel rod therethrough. Moreover, a plurality of elongated movable control rods slidably extend through preselected ones of the grid cells for controlling the fission process. A plurality of these fuel rod assemblies are grouped to define a nuclear reactor core, which is sealingly enclosed within a reactor pressure vessel. Liquid moderator coolant (i.e., demineralized water) is caused to flow past the rods of the fuel assembly for assisting in the fission process and for removing the heat produced by the fission process. During operation of the nuclear reactor, heat due to fission of the fuel material is carried from the fuel assemblies by the liquid moderator coolant flowing past the fuel rods in the fuel assemblies. The heat carried away by the liquid moderator coolant is ultimately transferred to a turbine-generator for generating electricity in a manner well known in the art of electrical power generation.
Each of the previously mentioned movable control rods is engaged by a control rod drive shaft capable of moving the control rod slidably through its associated grid. Each control rod drive shaft extends through an upper core plate and through an upper support plate that is spaced above the upper core plate, the upper support plate and the upper core plate being horizontally disposed in the reactor pressure vessel. The control rods that are engaged by the control rod drive shaft are slidably received in elongated thimble tubes disposed through the grid cells of each fuel assembly, which fuel assembly is in turn located below the upper core plate. Moreover, vertically extending through the upper support plate and the upper core plate are a plurality of elongated instrumentation tubes each having a longitudinal bore therethrough for receiving a probe carrier that caries an instrumentation probe to measure desired core physics quantities (e.g., neutron flux) in the reactor core.
Each instrumentation tube includes elongated portions having threaded ends to threadably connect the elongated portions of the instrumentation tube together. The instrumentation tube is segmented for ease of assembly when positioning it within the reactor pressure vessel. However, during normal operation of the reactor, the liquid moderator coolant circulating in the reactor pressure vessel causes vibration of the internal components, including the instrumentation tubes, which are disposed in the vessel. Moreover, off-normal operation caused by seismic events and postulated accidents (e.g., loss-of-coolant accident) also causes vibration of the internal components, including the instrumentation tubes. It is desirable to prevent any possibility of unthreading of the threaded ends of the instrumentation tubes during normal and off-normal conditions because such unthreading, that may be caused by these vibrations, may lead to the elongated portions of the instrumentation tube becoming disconnected at their threaded ends. Disconnection of the elongated portions of the instrumentation tube is undesirable because such disconnection may lessen the ability of the instrumentation tube to provide a clear and straight guideway for the probe carrier.
Therefore, a problem in the art has been to provide means for preventing unthreading of the threaded ends of the instrumentation tube when the instrumentation tube is subjected to vibrations caused by normal operating conditions and when the instrumentation tube is subjected to vibrations caused by off-normal operating conditions.
One prior art solution to this problem is to place weldments around the outside of the threaded ends belonging to the elongated portions of the instrumentation tube to provide additional assurance that the threaded ends will not unthread. However, the placement of such weldments is time consuming and hence costly. Moreover, during maintenance operations, disassembly of the instrumentation tube by unthreading the threaded end is made more difficult by the presence of the welds. Therefore, it is desirable to provide a means for preventing unthreading of the threaded ends of elongated portions of the instrumentation tube in a manner that does not require welding.
Apparatus for connecting the threaded ends of members together in a manner not necessarily requiring welding are known in the prior art. For example, an improved conduit and means for supporting the same is disclosed in U.S. Pat. No. 1,438,751 entitled "Conduit for Thermotemperature Circuits of Grain Tanks" issued Dec. 12, 1922 to Leonard H. Des Isles. This patent discloses a conduit formed of a plurality of pipe sections connected together by couplings. The exterior of adjacent ends of the pipe sections are formed respectively with right and left hand screw threads and the interior of the coupling is formed with corresponding right and left hand threads. The adjacent ends of the pipe sections are shaped so that when brought together they will interlock. When the pipe sections are joined together, their threaded ends are advanced within the coupling until they engage the correspondingly threaded portions of the coupling, after which, by turning the coupling, the ends of the pipe sections will be brought together until they interlock. According to this patent, when the pipe sections are joined together by the coupling, danger of the independent rotation of the sections is avoided and hence the loosening or disconnection of the sections is prevented. After the coupling is in position for use, the extreme ends of the coupling are upset or swaged so that these parts bear securely against the walls of the pipe sections. Although the Des Isles patent discloses a coupling that is swaged to join pipe sections, this patent does not appear to disclose a segmented instrumentation tube including a locking sleeve for interlocking the segments of the instrumentation tube, so that the threaded ends of the instrumentation tube do not unthread when subjected to vibration.
A joint effected between a section of pipe and a tubular coupling is disclosed in U.S. Pat. No. 2,001,204 entitled "Pipe Joint and Method of Making the Same" issued May 14, 1935 to James A. Long et al. This patent discloses a pipe and tubular coupling machined exteriorly and interiorly, respectively, to provide exact sizes for a shrink-fit or press-fit. The coupling is beveled at its ends. The pipe section is formed with an annular groove at a distance from the end thereof. The parts are assembled together with the beveled end of the coupling disposed opposite to the annular groove of the pipe section. In order to obtain press-fitting engagement between the pipe section and the coupling, the latter element is preferably shrunk upon the former element. After the parts have thus been assembled, a swaging operation is performed at the beveled end of the coupling to produce an inwardly directed annular boss which interlocks with the groove in the pipe section and forms therewith a fluid tight seal. Although the Long et al. patent discloses a pipe section and a coupling that are swaged together, this patent does not appear to disclose a segmented instrumentation tube including a locking sleeve for interlocking the segments of the instrumentation tube, so that the threaded ends of the instrumentation tube do not unthread when subjected to vibration.
Although the above-recited prior art disclose an instrumentation tube including elongated portions having threaded ends welded together, a conduit formed of pipe sections connected together by couplings, and apparatus for effecting a joint between a pipe section and a coupling, the above-recited prior art do not appear to disclose a segmented instrumentation tube including a locking sleeve for interlocking the segments of the instrumentation tube, so that the threaded ends of the instrumentation tube do not unthread when subjected to vibration.
Therefore, what is needed is a segmented instrumentation tube including a locking sleeve for interlocking the segments of the instrumentation tube, so that the threaded ends of the instrumentation tube do not unthread when subjected to vibration.